1. Field of the Invention
The invention relates to an optical recording system with optimal recording laser beam power control, more particularly to an optical recording system using a method and device for generating mark formation effectiveness signals to optimally control the power of a recording laser beam.
2. Description of the Related Art
To record information on an optical recording medium, a light source of an optical recording system, such as a laser diode that is driven by a laser driver circuit according to a write control signal, generates an incident recording light signal on the optical recording medium. To assure that data is correctly recorded, it is important that the laser output must be maintained at an appropriate power level. The optimal power control (OPC) technique is widely employed in determining the initial laser power of incident recording light signals. In an optical recording medium, there is a section called Power Calibration Area (PCA) which is reserved for power testing and calibration. Before the actual data is recorded on the medium, a predetermined data stream is written on the PCA using a series of laser light signals at different power levels. Then, the recorded records in the PCA are read back using normal read power and are analyzed to determine the optimum power. The recording power level that yielded the best recording quality in the PCA is selected as the optimum power level of incident recording light signals for recording the actual data on sections of the optical recording medium. In practice, for most optical recording systems, due to various factors affecting optical recording systems and optical recording media, such as changes in the thickness of recording dye layer and substrate characteristics of optical recording media, changes in recording points due to shifting in laser optical path length, the spatial position relationship of recording media with respect to the optical recording system, changes in recording characteristics of recording media due to temperature variations, etc., the optimum power level for generating the best incident recording light signal is prone to vary as well. Therefore, when the recording signal power is too low, information cannot be completely recorded. Furthermore, when the recording signal power is too high, damage to recorded tracks can occur.
U.S. Pat. No. 5,216,660 discloses an optical recording system that addresses the aforesaid problem. As shown in FIG. 1, the optical recording system 1 of U.S. Pat. No. 5,216,660 includes a laser light source 10, an optical detector 11, a first sample-hold circuit 12, a second sample-hold circuit 13, a timing controller 14, a first analog-to-digital (A/D) converter 15, a second analog-to-digital (A/D) converter 16, a processor 17, a laser driver circuit 18, and a digital-to-analog (D/A) converter 19. The laser light source 10 provides an incident recording light signal (IRL) (see FIG. 2A) for recording information on an optical recording medium 2. The laser light source 10 is generally a laser diode mounted on an optical pickup head (OPU) and is driven by the laser driver circuit 18 according to a write control signal. The optical detector 11 detects a reflected write pulse (WRF) (see FIG. 2B) that is a reflection of the incident recording light signal from the optical recording medium 2. The reflected write pulse (WRF) is provided to the first and second sample-hold circuits 12, 13 for sampling. With further reference to FIGS. 2C and 2D, the timing controller 14 provides first and second sampling pulses (tA, tB) to the first and second sample-hold circuits 12, 13, respectively, to control the time and duration of sampling by the sample-hold circuits 12, 13. Thus, as shown in FIG. 2B, the first sample-hold circuit 12 can be used to detect a higher power level (VA) of the reflected write pulse (WRF), whereas the second sample-hold circuit 13 can be used to detect a lower power level (VB) of the reflected write pulse (WRF) Thereafter, the higher and lower power levels (VA, VB) are converted into digital form by the first and second A/D converters 15, 16 for processing by the processor 17 to obtain the value of VA/(VA−VB). The value of VA/(VA−VB) is then subtracted from a target value Ma, and the resulting difference is converted into an analog control signal by the D/A converter 19 for controlling the laser driver circuit 18 to drive the laser light source 10 so that, when the effective output power of the laser light source 10 reaches a value Mb, VA/(VA−VB) is equal to Ma, as shown in FIG. 3. Through this closed-loop control scheme, the laser light source 10 outputs an optimal effective power Mb.
The following are some of the drawbacks of the aforesaid conventional optical recording system 1:
1. Ideally, the first sample-hold circuit 12 samples a maximum power level of the reflected write pulse (WRF). In practice, the timing of occurrence of the peak value of the reflected write pulse (WRF) is not fixed, and is actually subject to change according to various factors, such as changes in the thickness of recording dye layer and substrate characteristics of optical recording media, skewing of the optical recording medium, etc. Since the time of sampling by the first sample-hold circuit 12 is fixed, and since the actual occurrence of the peak value of the reflected write pulse (WRF) is instantaneous, the first sample-hold circuit 12 is usually unable to detect the peak value of the reflected write pulse (WRF).
2. The first and second sample-hold circuits 12, 13 are coupled to the first and second A/D converters 15, 16, respectively. When additional sample-hold circuits are installed to increase the number of sampled values of the reflected write pulse (WRF), a corresponding increase in the number of the A/D converters will be required as well. This not only results in increased manufacturing costs, but also complicates the entire circuit configuration.